doribeans wrote:
I'm sorry that this isn't a serious question but...
isn't human exploration of tunnels on other planets the subject of about half of scary sci-fi thrillers?
- "it seems such an obvious thing."
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THE FIRST MEN IN THE MOON by H.G. Wells (1901) Chapter 13
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"We are some way in," he said. "I mean—perhaps a couple of thousand feet or more."
"Why?"
"It's cooler. And our voices are so much louder. That faded quality—it has altogether gone. And the feeling in one's ears and throat."
I had not noted that, but I did now.
"The air is denser. We must be some depths—a mile even, we may be—inside the moon."
"We never thought of a world inside the moon."
"No."
"How could we?"
"We might have done. Only one gets into habits of mind."
He thought for a time.
"Now," he said, "it seems such an obvious thing."
"Of course! The moon must be enormously cavernous, with an atmosphere within, and at the centre of its caverns a sea.
"One knew that the moon had a lower specific gravity than the earth, one knew that it had little air or water outside, one knew, too, that it was sister planet to the earth, and that it was unaccountable that it should be different in composition. The inference that it was hollowed out was as clear as day. And yet one never saw it as a fact. Kepler, of course—"
His voice had the interest now of a man who has discerned a pretty sequence of reasoning.
"Yes," he said, "Kepler with his sub-volvani was right after all."
"I wish you had taken the trouble to find that out before we came,"
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https://en.wikipedia.org/wiki/Phobos_(moon)#Shklovsky.27s_.22Hollow_Phobos.22_hypothesis wrote:
<<Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky, studying the secular acceleration of Phobos's orbital motion, suggested a "thin sheet metal" structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin. Shklovsky based his analysis on estimates of the upper Martian atmosphere's density, and deduced that for the weak [aerodynamic] braking effect to be able to account for the secular acceleration, Phobos had to be very light—one calculation yielded a hollow iron sphere 16 kilometers across but less than 6 cm thick. In a February 1960 letter to the journal Astronautics,
[climate change denier] Fred Singer, then science advisor to U.S. President Dwight D. Eisenhower, said of Shklovsky's theory:
If the satellite is indeed spiraling inward as deduced from astronomical observation, then there is little alternative to the hypothesis that it is hollow and therefore Martian made. The big 'if' lies in the astronomical observations; they may well be in error. Since they are based on several independent sets of measurements taken decades apart by different observers with different instruments, systematic errors may have influenced them.
Subsequently, the systemic data errors that Singer predicted were found to exist, and the claim was called into doubt, and accurate measurements of the orbit available by 1969 showed that the discrepancy did not exist. Singer's critique was justified when earlier studies were discovered to have used an overestimated value of 5 cm/yr for the rate of altitude loss, which was later revised to 1.8 cm/yr. The secular acceleration is now attributed to tidal effects, which had not been considered in the earlier studies.
The density of Phobos has now been directly measured by spacecraft to be 1.887 g/cm3. Current observations are consistent with Phobos being a rubble pile. In addition, images obtained by the Viking probes in the 1970s clearly showed a natural object, not an artificial one. Nevertheless, mapping by the Mars Express probe and subsequent volume calculations do suggest the presence of voids and indicate that it is not a solid chunk of rock but a porous body. The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third being empty.>>
An Unusual Hole in Mars
